Typescript: Function accepting 2 Types but property doesn’t exist on one of the types

I have a function that takes 2 types.

handleDragging(e: CustomEvent<SelectionHandleDragEventType | GridHandleDragEventType>) {
    e.stopPropagation();

    const newValue = this.computeValuesFromPosition(e.detail.x, e.detail.y, e.detail.variant);

    // other same code
})

the issue is that GridHandleDragEventType does not have a variant as part of the type. In those cases, I don’t mind sending null but I keep getting the TS issue:
Property 'variant' does not exist on type 'GridHandleDragEventType'. Is there a clean way to resolve this?